Optimal Control for AWS-Based Wave Energy Conversion System

Archimedes wave swing (AWS)-based wave energy conversion (WEC) is the first device adopting the direct-drive power takeoff. The linear permanent magnet generator (LPMG) is employed to convert the wave energy to electric power. In this paper, the power characteristics of the LPMG are discussed in detail using the model in the $dq0$ reference frame established by the authors in a previous work and the forces acting on the translator of the AWS from the LPMG are analyzed. Then based on the two resonance conditions in the $dq0$ coordinates, an optimal control strategy for both stiffness and damping, fully using the generator side power electronic converter, is proposed to regulate the AWS in resonance with the wave, so as to extract the maximum power. In contrast to the mechanical resonance regulation approach for stiffness control, the resonance regulation approach for both stiffness and damping control proposed is much easier to implement and much faster. A supplementary DC voltage control for the grid side converter controller is proposed to maintain the voltage level of the DC-Link. Simulations are performed to evaluate the effectiveness of the controllers proposed and to demonstrate the control capability of the controllers under constant waves as well as variable waves.